The present invention relates to thermal shock protection during initial heat up stages for electrodes of an electrolytic cell operating at an elevated temperature. Electrodes of the type requiring thermal shock protection by the method and apparatus of the present invention are described in Foster et al U.S. Pat. No. 4,071,420 issued Jan. 31, 1978. In a preferred embodiment, the cathodes of the Foster et al patent are hollow cylindrical bodies of sintered TiB.sub.2 protruding out of a metal pad toward the anode. While the cathodes of the Foster et al patent are highly effective for the production of aluminum after being heated to an elevated operating temperature, it has been found in practice that such cathodes tend to be brittle and subject to cracks and breakage if not protected from thermal shock in the initial heat up or start up stages by the method and apparatus of the present invention.
A form of thermal shock protection for TiB.sub.2 electrodes during start up of an electrolytic cell is shown in Colley British Pat. No. 1,046,705, issued Oct. 26, 1966. In FIG. 5 and on pages 2-4 of the specification, Colley discloses an insulating layer around each refractory metal element comprising a one-half inch thick layer of powdered alumina. In a preferred embodiment, the insulating layer is retained in an aluminum container that melts away at cell operating temperatures. However, the Colley patent fails to teach the desirability of providing a metal heat dispersing means having a melting point at least approximating the operating temperature of the cell, as disclosed and claimed herein. The refractory metal electrodes shown in the Colley patent are solid rather than hollow so that the need for a heat conductor means inserted within a cavity in a hollow body electrode during start up is not suggested by Colley.
It is a principal object of the present invention to provide a method and apparatus for protecting electrodes from cracks and breakage accompanying thermal shock during initial heat up of an electrolytic cell for production of a metal at an elevated operating temperature.
It is a related object of the invention to provide a method and apparatus for protecting electrodes of an electrolytic cell during heat up to an elevated operating temperature, wherein the materials providing protection are compatible with efficient operation of the cell after the operating temperature has been reached.
Further objects of the invention are to provide a heat conductor means for insertion into a cavity in a hollow cathode of an electrolytic cell; to provide an insulating means protecting a hollow cathode from thermal shock during initial heat up stages of an electrolytic cell; and to provide a heat dispersing means for minimizing temperature differences between various locations on the hollow cathode when the interior of an electrolytic cell is heated by an auxiliary heat source.
Additional objects and advantages of the invention will become apparent to persons skilled in the art from the following specification taken in conjunction with the drawings.